• Repeat the keyword as many times as possible in the ad text.
• Delete the keyword and add the keyword to the campaign again
• Increase the daily budget for the campaign in which the keyword is located
• Modify the ad associated with that keyword to direct to a highly-relevant landing page

The correct answer is: Modify the ad associated with that keyword to direct to a highly relevant landing page

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Explanation: In order to increase the Quality Score of a low-performing keyword, you must modify the ad associated with that keyword to direct it to a highly relevant landing page. You’ll want to improve the relevance of your keywords to help boost their Quality Scores or modify the match type for ones that aren’t helping you meet your advertising goals, or delete duplicate keywords in your account.

Read more here: https://support.google.com/google-ads/answer/2453976